1. Field of the Invention
The invention relates to an improved disc brake for vehicles such as snowmobiles, off-road utility vehicles, or agricultural vehicles, and for machinery driveshaft braking systems. More particularly, the invention relates to automatic adjustment apparatus for such disc brakes.
2. Description of the Prior Art
Prior art disc brakes of the type described above frequently include a push rod that translates in an axial direction to urge friction elements into frictional engagement with a rotor. The push rod in such brakes is typically threaded externally and has a rotatable annular nut threaded thereon. The annular nut and push rod assembly is generally urged in a brake-applying axial direction by a rotatable actuating member actuated by the operator through a linkage mechanism.
Such prior art brakes are adjusted by rotating the annular nut with respect to the push rod in response to excessive friction element wear, thereby axially advancing the push rod relative to the annular nut. Rotation of the annular nut is typically accomplished by a ratchet assembly between the rotatable actuating member and the annular nut. The ratchet assembly effects rotation of the annular nut after a predetermined over-rotation of the actuating member resulting from excessive clearance between the friction elements and the rotor.
Prior art disc brakes employing ratchet-type adjustment assemblies perform brake adjustments only after the friction elements have worn sufficiently to cause a pawl to advance to the next tooth on the ratchet wheel. Thus, such adjustment assemblies typically allow too much friction element wear to occur before an adjustment is made. Ratchet-type adjustment assemblies also require too great a stroke of the actuating member in order to function. Finally, the ratchet assembly typically must be at least partially disassembled before manually retracting the push rod in order to install new friction elements.